From day one, Instagram’s main priority has been building a great experience on its iPhone app — not on the web. But as it turns out, the photo-sharing service has become a huge web destination anyway: Instagram’s website is currently receiving 10 million page views each day, adding up to some 300 million page views per month, co-founder Kevin Systrom told GigaOM.

Such numbers would be impressive for any service, but they’re especially interesting given that the Instagram experience is so tailored to users of the app (currently available only on the iPhone), not viewers on the web. For example: If you don’t have an Instagram account, you can only look at individual Instagram photos people link to — you can’t click around on the site to see users’ full photo galleries or other personal profiles. (There are third-party services such as Hashgram that let you search and see photo galleries.) While photo services such as Flickr have been built to facilitate public web browsing, Instagram as it is now is a mobile service. Yet despite all these access hurdles to the general public, Instagram is fielding some crazy web traffic.

And it’s very possible that Instagram still has a lot of growth ahead. On Friday, the company launched the ability for people to share full-sized Instagram photos within Facebook and create Facebook albums of Instagram photos. Now, this could theoretically cause Instagram’s web traffic to take a dip, but the company’s hope is that it will ultimately lead to more growth, as it could give Instagram more visibility beyond the hip early adopter crowd and increase awareness among mainstream web users. Meanwhile, the debut of Instagram for Android is on deck for 2012, which could lead to a another big user growth spike for the service.